This application relates to a method and apparatus for the protection of electrical equipment from high voltage transients.
The sudden failure or gradual step by step deterioration of electrical equipment due to high voltage transients or surges stemming from natural or man made occurrences has long been recognized as a serious problem in the electrical industry. The literature has reported many investigations of transient voltage occurrences on a wide variety of power distribution systems, both residential and commercial. These studies have shown that voltage spikes of 6 KV or more are not uncommon on residential lines with voltage surges of 100 KV or more in many high power industrial systems. An even worse situation is reported for remote rural power distribution systems of the type normally used to supply electric power to oil fields. Specifically, the down hole pump motors and their associated feeder cables, which are often used at these remote pumping sites are particularly susceptible to electrical failure. Transients generated from such factors as lightning, line switching or full voltage starting can easily damage the down hole motor and/or its very long feeder cable; since the installation is usually heavily grounded to earth through either direct contact with the metallic well casing or conduction through low impedance salt water in the well bore. Moreover these pump motor and feeder cable systems may be damaged not only by high transient voltage levels but also by high rates of rise of voltage as well.
Experience has shown that in such circumstances motor and/or feeder cable failure becomes a very common occurrence, leading to expensive shut down time and replacement. Consequently an effective and economic method of surge and transient protection is urgently required for installation such as these. The present invention offers a solution to this problem. It should be noted, however, that the device would be effective in many similar applications where transients can degrade or damage power transmission or other associated equipment.
Surge or transient suppressors are by no means new devices, since they have been used in the electrical industry for many years. The communications industry in particular has of necessity utilized transient suppression gear on equipment from the outset because of the delicate nature of electronic hardware in general. Power utilities have also, but to a much lesser degree, incorporated various forms of lightning arrestors in their distribution systems, particularly newer ones. However, whereas these lightning arrestors have in general provided adequate protection for the power companies' equipment, they have often been ineffective in providing transient protection for the subscriber; especially under circumstances previously outlined herein.
Conventional methods of protection usually consist of providing a station class lightning arrestor in combination with a separate surge compacitor mounted in close proximity to the motor terminals (usually not more than 50 feet away). This method, though effective in most industrial motor installations, does not provide adequate protection for submergible oil well pump installations, due primarily to the long feeder cable and severe down hole space and environmental conditions.
U.S. Pat. No. 3,824,431, issued to Schlicke illustrates a system applicable to the surge protection of communication transmission lines. U.S. Pat. No. 408,483 issued to Golde et al relates to a similar type of surge protection as the present invention. In both cases, use is made of some elements utilized in the present case. As such, the patents are typical of the prior art.
The present invention differs significantly from these and all other suppressor systems of which the applicant is aware.